Our goal is to measure frequencies of point mutations in sperm from mice treated with mutagens. Our strategy for detecting mutations is based on immunologic differences in a sperm-associated isoenzyme, lactate dehydrogenase-C (LDH-C) existing as isomeric forms immunologically identifiable to each species (i.e., mouse, rat, humans). Normal antibody to rat LDH-C does not react with LDH-C associated with mouse sperm; however, low frequencies of mouse sperm contain LDH-C that reacts with antibody in rat LDH-C. Moreover, mice treated with a mutagen procarbazine generate increased frequencies of sperm that react with antibody to rat-form LDH-C. The increased frequency of mouse sperm expressing rat-form LDH-C increases linearly with increasing doses of procarbazine. Monoclonal antibodies coupled with fluorescent markers will be utilized whereby mouse sperm cells will be screened. Mutants which are identified will be sorted to confirm that variant sperm express mutant forms of LDH-C. Once the tests are validated, studies will be extended to monitor frequencies of mutant forms of LDH-C in sperm from humans with clinical histories of treatment or exposure to suspected mutagens.